Equine Herpesvirus 

Myeloencephalopathy Incident

Guidelines for State Animal Health 

Officials

Revised January 2018
IDOHC EHM Incident Guidance Document

2

Revised January 2018
IDOHC EHM Incident Guidance Document 3

Revised January 2018

Table of Contents

Introduction .........................................................................................................................4

Definitions ...........................................................................................................................6

Diagnostic Testing ...............................................................................................................9

Quarantine Placement ......................................................................................................17

Quarantine Release ...........................................................................................................23

Investigation ......................................................................................................................26

Biosecurity Recommendations ........................................................................................28

Communication .................................................................................................................32

Vaccination ........................................................................................................................37

Appendix ............................................................................................................................39

References...........................................................................................................................55
IDOHC EHM Incident Guidance Document 4

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Introduction

On October 19, 2013, the American Association of Equine Practitioners Foundation (AAEP) and

the United States Animal Health Association (USAHA) Committee on Infectious Diseases of Horses

(IDOHC) sponsored an Equine Herpesvirus-1 (EHV-1) Workshop. The workshop identified a need

for regulatory consensus on case definition, outbreak definition, quarantine parameters,

diagnostic testing and biosecurity practices for Equine Herpesvirus Myeloencephalopathy

incidents. USAHA IDOHC established an EHV-1 subcommittee to develop a consensus document

related to the EHV-1 regulatory mitigation.

This document represents an updated version of the original guideline developed by the 

subcommittee. (Updated in January 2018).

The EHV-1 Subcommittee members participating in updating this document included:

1. Rory Carolan – USDA-APHIS-VS-SPRS

2. Ann Dwyer – American Association of Equine Practitioners

3. Alexandra Eckhoff – New Mexico Livestock Board

4. Joe Fisch-Florida Dept of Agriculture

5. Katie Flynn – California Dept. of Food and Agriculture (2015 Subcommittee chair)

6. Rusty Ford – Kentucky Dept. of Agriculture

7. Kent Fowler – California Dept. of Food and Agriculture

8. Tim Hanosh – New Mexico Dept. of Agriculture

9. Carl Heckendorf – Colorado Dept. of Agriculture

10. Mike Herrin – Oklahoma Dept. of Agriculture

11. Angela Pelzel-McCluskey – USDA-APHIS-VS-SPRS

12. Keith Roehr – Colorado Dept. of Agriculture

13. Alma Roy – Louisiana State University

14. Abby Sage – VA Dept. of Agriculture and Consumer Services

15. Mike Short – Florida Dept. of Agriculture

16. Andy Schwartz – Texas Animal Health Commission

17. Tracy Sturgill – USDA APHIS VS NVSL

18. Peter Timoney – Gluck Equine Research Center

19. Josie Traub- Dargatz – USDA-APHIS-VS-CEAH and Colorado State University

20. Cliff Williamson – American Horse Council

21. Kenton Morgan – Eq Technical Services, Zoetis (2017 Subcommittee chair) 

During Equine Herpesvirus Myeloencephalopathy (EHM) incidents, the state animal health

officials’ (SAHO) goal is to prevent the spread of the disease agent, specifically Equine Herpesvirus1. Science-based disease control protocols, adapted to the specific incident, control disease

spread while ensuring compliance and minimizing the impact on equine movement. There is no

single protocol that can be applied to all EHM incidents as there are multiple factors that must be

considered when determining the optimal disease containment response. This guidance
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document provides SAHOs, with science and field experience based control guidance to be

considered during an EHM incident. This guidance document is an evolving document.

Questions or concerns regarding this document can be directed to the chair or vice chair of the 

Committee on Equine. For committee chair or vice chair contact information visit: 

http://www.usaha.org/committees
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DEFINITIONS

Assumption: The definitions are intended to be utilized during an EHM incident. The document is 

based on diagnosis or suspicion of one or more Equine Herpesvirus Myeloencephalopathy (EHM) 

cases.

EHM Incident: Detection of one or more confirmed cases of EHM, and where there is confirmation 

of disease agent spread or evidence of potential for disease transmission from an EHM confirmed 

case to additional horses in a population.

Index Definitions:

1. Confirmed Index EHM Case: A horse displaying signs of central nervous system (CNS) 

dysfunction, including but not limited to hindlimb incoordination, weakness, recumbency and/or 

urinary bladder atony, with evidence of infection with any strain of EHV -1 based on virus isolation 

and /or PCR testing of nasopharyngeal/nasal swab or blood (buffy coat) specimens. If the horse dies 

or is euthanized, the case can be confirmed based on histological evidence and detection and/or 

demonstration of EHV-1 in CNS tissues collected at necropsy.

2. Suspect Index EHM Case: Highly suggestive EHM case, defined as a horse displaying signs of 

central nervous system (CNS) dysfunction, including but not limited to hindlimb incoordination, 

weakness, recumbency and/or urinary bladder atony which may have been preceded by fever, 

respiratory signs and/or abortion in horses on the premises. 

3. Index EHM Premises: The premises on which the index EHM case has occurred.

4. Index Point of Exposure: Initial site of exposure to EHV-1 for the confirmed index EHM case 

and/or suspect index EHM case as determined by an epidemiologic investigation. In cases of 

presumed reactivation of latent virus, a point of exposure for the index case does not exist.

Subsequent Definitions:

1. Exposed horse: A horse with direct or indirect contact with the EHM confirmed index case 

within the 14 days preceding the onset of neurologic signs or a horse that potentially had direct 

or indirect contact with horses at the point of exposure of the index case within the preceding 

14 days. (For details on exposure risk, see investigation section).

2. Suspect EHV-1 case: An exposed horse that shows no neurologic signs but displays some of the 

clinical signs consistent with EHV-1 infection; these may include fever (rectal temperature 
IDOHC EHM Incident Guidance Document 7

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greater than 101.5°F), limb edema, abortion or nasal discharge during the 14 days after initial 

exposure to a confirmed EHM case.

3. Confirmed EHV-1 case: A horse that is showing no neurologic signs but tests positive for EHV-1 

by virus isolation and/or PCR testing of nasopharyngeal/ nasal swab or blood (buffy coat) or 

fetal tissue specimens along with clinical signs consistent with EHV-1 infection, such as fever, 

limb edema, abortion or nasal discharge. If the horse dies or is euthanized, the case may be 

confirmed based on histological evidence and detection and/or demonstration of EHV-1 in 

tissues collected at necropsy. 

4. Suspect EHM case: An exposed horse that develops neurologic signs suggestive of EHM, 

including but not limited to hindlimb incoordination, weakness, recumbency and/or urinary 

bladder atony during the 14 days prior to the index EHM case developing clinical signs and/or 14 

days after the last potential exposure to the confirmed EHM case.

5. Confirmed EHM case: A horse which is positive for any strain of EHV-1 by virus isolation and /or 

PCR testing of nasopharyngeal/nasal swab or blood (buffy coat) specimens along with the 

presence of clinical signs consistent with EHM. If the horse dies or is euthanized, the presence of 

histological lesions and/or demonstration of EHV-1 in the CNS tissues collected at necropsy is 

confirmatory of a diagnosis.

6. Non-clinical test positive case: An exposed horse that is not exhibiting clinical signs (afebrile, 

non-neurologic) but tests positive for any strain of EHV-1 by virus isolation and/or PCR testing of 

nasopharyngeal/nasal swab or blood (buffy coat) specimens. 

a. Note: during any given incident some horses may start in this category before 

developing neurologic signs and subsequently being confirmed as an EHM case 

after they develop neurologic signs.

7. EHM Premises: A premises where a confirmed or suspect case of EHM currently resides or a 

premise where an EHM case resided within the preceding 14 days.

8. Fever: Body temperature of 101.5° F or greater. 

9. Afebrile: Body temperature of less than 101.5° F in a monitored horse.

10. Monitored horse: A horse that is being evaluated for any evidence of clinical signs consistent 

with EHV-1 infection. A monitored horse should have the body temperature determined at 
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least twice a day e.g. morning and evening in order to detect a fever and it should be examined 

for any neurologic signs. A horse cannot be considered to be truly monitored for EHV-1 induced 

fever if it has been treated with a non-steroidal anti-inflammatory drug (NSAID) within the 

previous 24 hours.

11. ORF: Open Reading Frame

12. SNP: Single nucleotide polymorphism

13. PPE (Personal Protective Equipment): Any protective clothing, garment, footwear or equipment 

designed to protect the wearer from direct exposure to infectious agents. Proper use and 

disposal of these garments will reduce the spread of infectious agents.

14. EHV-1 “A” strain: Any strain of EHV-1 having the SNP genetic marker ORF 30 A2254 genotype. 

(Previously referred to as wild strain or non-neuropathogenic strain).

15. *EHV-1 “G” strain: Any strain of EHV-1 having the SNP genetic marker ORF 30 G2254 genotype. 

(Previously referred to as mutated or neuropathogenic strain).

* Strains of EHV-1 having this genotype have on occasion been associated with severe 

outbreaks of EHM. In clinical trials, such stains have been associated with a higher level of 

viremia than strains with the ORF 30 A2254 genotype. Strains of the EHV-1 with the ORF 

30 G2254 genotype have also been referred to as mutant strains of EHV-1. This is a 

misleading term since such strains of EHV-1 were detected in archival samples from the 

1970’s and accordingly they should not be referred to as newly mutated forms of EHV-1. 

16. Exposed premises: The physical location where an index case or an EHV-1 exposed horse has 

been in the previous 14 days, to include but not limited to pastures, event venues, training 

facilities, and breeding facilities. Note: The extent of the area of premises exposed needs to be 

based on a thorough epidemiologic evaluation.

NOTE: 

Non-neuropathogenic or wild strain of EHV-1: Any strain of EHV-1 with the ORF 30 A2254 genotype. 

Neuropathogenic or mutant strain of EHV-1: Any strain of EHV-1 with the ORF 30 G2254 genotype. 

“Non-neuropthogenic EHV-1 strain” and “neuropathogenic EHV-1 strain”; are terms that lead to 

confusion since both strains have the potential to cause EHM. In an outbreak environment knowing 

which strain is present does not necessarily change what needs to be done to control/mitigate the 

situation.
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DIAGNOSTIC TESTING

Serologic Testing

Due to the likelihood of widespread exposure to EHV-1 and the common practice of vaccination of 

the general equine population against this virus infection, serologic testing at a single point in time 

is uninformative and of very limited diagnostic value. The serologic test readily available in the 

United States is the virus neutralization test (VNT); some other countries however, have the 

availability to use the complement fixation test (CFT) which can be used to detect recent exposure 

to EHV-1. Serologic testing, namely using the VNT, which demonstrates seroconversion or a fourfold or greater increase in serum antibody titers between samples collected 10- 21 days apart, 

provides presumptive evidence of recent EHV-1 infection assuming EHV-1 vaccination has not taken 

place just prior to or during that time period. EHV neutralizing tests (VNT) do not distinguish 

between EHV-1 and EHV-4 antibodies.

However, type specific ELISA tests based on a portion of the glycoprotein G of each virus have been 

developed. The CFT and ELISA type specific antibody detection tests are not currently available at 

diagnostic laboratories in North America.

Virus Detection

Virus isolation is considered the gold standard for confirmatory laboratory diagnosis of EHV-1 

infection, although the time required to obtain a positive result limits its value for outbreak 

management. Virus identification of EHV-1 by isolation from nasal or nasopharyngeal swabs or 

buffy coat samples is confirmatory evidence of a diagnosis of EHM in a horse with compatible 

clinical signs.

The polymerase chain reaction (PCR) has become the diagnostic test of choice due to its high 

analytical sensitivity and specificity and rapid turn-around time. Positive PCR results can be 

obtained when virus isolation is negative due to sub-detectable levels of infectious virus, 

inactivated virus or presence of viral nucleic acid. PCR tests carried out simultaneously on both 

nasal secretions and buffy coat samples are useful in establishing the stage of infection in an 

animal. Quantitation of genomic DNA level is used as a guide in assessing the potential of a horse 

with nasal shedding EHV-1 to transmit infection. Viremia is the presence of virus (intact and 

regarded as infectious) in the bloodstream. Although viremia is an essential component in the 

pathogenesis of EHM, some studies have failed to show that the level of viremia is directly 

correlated with level of risk for development of EHM. Other studies have shown correlation of a 

high level of viremia with more severe CNS diseases. While the level of virus detected by PCR

indicate the presence or absence of viral DNA in the specimen tested, at this time that level of virus 

has not been correlated with the severity of clinical presentation and cannot be used to predict 
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clinical outcome. The lack of standardization of test methods between laboratories and the lack of 

standardized use of quality assurance controls amongst laboratories remain an ongoing challenge in 

test interpretation.

Note: Virus isolation is optimized when samples are collected and shipped the same day and are 

received by the laboratory within 24 hours of collection.

Recently, antiviral drugs have been used by some for the treatment of EHM cases. Currently, there 

is ongoing research regarding the use of antiviral drugs for treatment of neurologic cases and even 

prevention of EHV-1 infection in exposed horses. Theoretically, use of antivirals could alter level of 

viremia and viral shedding and thereby have an impact on test results. However, at this time there 

is not enough science based literature available to determine the impact of the use of antiviral 

drugs on the level and duration of viremia and nasal shedding of virus. Still, it should be considered 

during the evaluation of test results, therefore it is important that the submitter record treatment 

with antiviral drugs on the submission form.

Types of PCR tests

• Conventional/Standard PCR: The amplified DNA is detected at the end of the test 

procedure. This test is of more limited sensitivity and is non-quantitative.

• Nested PCR: Two sets of primers are used in two successive PCRs. The amplified DNA 

fragments are used in a second PCR for identification. It is a very sensitive assay but is 

associated with the risk of cross-contamination between samples.

• Real Time PCR: the amplified DNA is detected as the reaction progresses. More sensitive, 

specific, rapid and reliable than conventional PCR. This test allows for determination of the 

amount of viral nucleic acid in the sample being tested.

EHV-1 PCR Tests

The glycoprotein B gene PCR assay is often used as a screening test to detect EHV-1; a positive test 

indicates EHV-1 infection. However, this test cannot differentiate EHV-1 G strains (previously 

referred to as mutant strain) from the EHV-1 A strains (previously referred to as wild strain). 

Subsequent subtyping based on the DNA polymerase gene assay, which targets the single 

nucleotide polymorphism at position 2254 of the virus open reading frame 30 which encodes for 

the catalytic subunit of the DNA polymerase gene, can differentiate G and A virus strains. Some 

laboratories may only use the DNA polymerase gene assay for screening for EHV-1 infection.
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Characteristics of an Ideal PCR Protocol

Consider these characteristics of PCR assays when choosing the most appropriate type of test to 

meet your needs and that are consistent with the reason for testing in your situation:

1. Sensitivity: Does the assay have a high sensitivity and specificity for the detection of EHV1? Is strain typing necessary? Certain highly sensitive PCR assays can differentiate EHV-1 G 

strains (previously referred to as mutant strains) from EHV-1 A strains (previously referred 

to as wild stains) in a sample.

2. Timeliness: Can the laboratory provide timely results necessary for confirmation of 

infection? Assay results can be available within 12 hours of sample receipt at some 

laboratories.

3. Quantitative Load: Can the assay provide quantitative results? Will quantitative results be 

useful in the epidemiologic investigation or disease control efforts? A quantitative PCR 

assay can provide quantitation of viral DNA in a specimen.

Additional considerations when choosing an appropriate laboratory for sample testing:

1. Turn-around Time: Can the laboratory provide a rapid turnaround time? A laboratory 

which can provide timely reports to the practitioner is beneficial.

2. Laboratory Assistance: Does the laboratory have readily available personnel to assist with 

interpretation of test results? A more detailed understanding of a positive or negative test 

result can assist in the implementation of appropriate biosecurity and infection control 

measures.

3. State Animal Health Official Acceptance: Will the state animal health official accept the 

results from the laboratory being considered for sample submission? Some animal health 

officials require that official test results be provided by specified laboratories and may 

require additional sample types to be collected and tested, such as collection and testing 

a different source of sample from a previously tested horse, e.g. blood versus nasal swab 

or sampling of additional horses in an incident.
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Recent EHV-1 PCR Ring Trial Study

Abstract from 2014 USAHA IDOHC Meeting, San Diego, CA -

http://usaha.org/Committees/InfectiousDiseasesOfHorses.aspx

“In 2013, the USDA-APHIS National Veterinary Services Laboratory (NVSL) and American Association 

of Veterinary Laboratory Diagnosticians (AAVLD) conducted a joint inter-laboratory comparison 

(ring trial) of equine herpesvirus type 1 (nEHV-1) polymerase chain reaction (PCR) techniques in an 

effort to standardize testing methodology for equine herpesvirus myeloencephalopathy (EHM) 

carried out at state/university/provincial diagnostic facilities in North America.

A total of 28 state diagnostic facilities from the USA and Canada evaluated a ring test “panel” of 

field EHV isolates. The 28 participating laboratories used 38 different procedures (some laboratories 

tested by multiple procedures) based upon modifications of 10 peer-reviewed published methods 

for EHV-1 PCR. Two genes were utilized as PCR targets, the EHV-1 glycoprotein B gene, and the EHV1 ORF 30, viral DNA polymerase gene. Glycoprotein B gene- based PCR assays, which are 

fundamentally designed as screening assays that detect wild-type (wt-EHV-1) and neuropathogenic 

(nEHV-1)strains, were used by 15 participating laboratories and had excellent diagnostic sensitivity 

for both wt-EHV-1 (100%; 30/30 samples identified correctly), and nEHV-1 (98.8%; 89/90 samples 

identified correctly), as well as excellent diagnostic specificity (98.3%; 59/60 non-EHV-1 samples 

identified correctly). As predicted, none of the glycoprotein B gene-based assays differentiated wtEHV-1 from nEHV-1 and as such serve as excellent diagnostic tools to identify EHV-1 infected horses 

from non-EHV-1 infected horses but do not identify nEHV-1 specifically. ORF 30 (viral DNA 

polymerase) gene-based PCR assay had more variable results from testing of the ring trial samples. 

Three published ORF 30 A/G 2254 assays: 1) Allen et al, 2007, 2) Pusterla et al, 2009, and 3) Smith et 

al, 2012), which differentiate wt-EHV-1 from nEHV-1 by detecting the A2254 (wt-EHV-1) or G2254 

(nEHV-1) polymorphism, were used by 21 participating laboratories. The three assays had 

diagnostic sensitivity (based upon correct identification of nEHV-1 samples) of 93.1% (67/72 

samples, Allen 2007), 100% (36/36 samples, Pusterla 2009) and 94.4% (17/18 samples, Smith 2013). 

The diagnostic specificity (based upon correct identification of non-nEHV-1 samples) was 88.9% 

(64/72 samples, Allen 2007), 72.2% (26/36 samples, Pusterla 2009), and 100% (18/18 samples, 

Smith 2013).”
IDOHC EHM Incident Guidance Document 13

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Considerations when using PCR testing for EHV-1

1. Testing horses with clinical signs:

Horses with high fevers and/or other clinical signs including coughing or mild nasal 

discharge, or abortion, with or without neurologic signs, should be tested for EHV-1 by PCR, 

preferably by real time or nested PCR, if other possible causes for these signs are not 

apparent.

2. Screening of clinically normal horses with a link to an EHV outbreak:

The use of testing for EHV-1 in horses that are clinically normal but that have some link to an 

EHV outbreak will be discussed later.

3. Screening of horses in the general population:

Historically the EHV-1 test has been performed on horses as a screening test for entry to 

events and as a requirement for entry to boarding facilities or as part of a purchase 

examination. It is not recommended that testing as described above (screening of horses in 

the general population) be performed. Since EHV-1 is considered to be endemic in most 

horse populations and detection of the virus in nasal secretions is likely a transient 

occurrence that results in an undefinable risk for spread of disease.

Necropsy of Suspect EHM Horses

A necropsy provides an important means of confirming the presence of EHV-1 neurologic disease. 

EHM is not a zoonotic disease but consideration should be given to other diseases with the 

potential for zoonotic implications such as rabies. Thus, it is important to use appropriate biosafety 

measures during necropsy examination. It is important to necropsy suspect EHV-1 cases as there 

are documented cases of suspect EHM horses with negative ante-mortem EHV-1 test results on 

nasopharyngeal/nasal swab and buffy coat samples that were confirmed positive for EHV-1 related 

neurologic disease on necropsy examination.

Therefore, necropsy examination of a horse with neurologic disease that dies or has to be 

euthanized is recommended. To ensure appropriate samples are taken at necropsy, individuals are 

reminded to alert the pathologist of the suspect EHM status of the case and provide the neurologic 

history on the laboratory submission forms. 

Appropriate Timing of Sample Collection

Correct selection of horses for sampling within an affected group is vital to gain the best- quality 

information for the epidemiologic investigation and disease control efforts. Samples collected 

represent a single point in time, as viral shedding changes over the course of the infection. Viral 

shedding from the respiratory tract of adult horses is detectable typically for less than 10 days and 

may be intermittent. The optimal window for nasal swab sampling is at the onset of clinical signs. In 

some situations, where initial testing was negative for EHV-1 but EHV infection is suspected as the 
IDOHC EHM Incident Guidance Document 14

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cause of disease, it is recommended to repeat sampling within 2 to 4 days of onset of clinical signs. 

The amount of EHV-1 DNA detected in nasal swabs varies from horse to horse and over the course 

of disease in a given animal and does not necessarily correlate with the severity of disease.

Figure courtesy of Dr. Lutz Goerhrig, extracted from 2nd Edition of Equine Neurology. 
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Recommended Horses to Test during an EHM Incident

1. Suspect Index EHM Horses: Highly suggestive EHM case, defined as a horse displaying 

signs of central nervous system (CNS) dysfunction, including but not limited to hindlimb 

incoordination, weakness, recumbency and/or urinary bladder atony which may or may 

not have been preceded by fever, respiratory signs and/or abortion in other horses on the 

premises.

2. Suspect EHM Horses: An exposed horse displaying signs suggestive of EHM including, but 

not limited to hindlimb incoordination, weakness, recumbency and/or urinary bladder 

atony during the 14 days prior to the index EHM case developing clinical signs and/or 14 

days after last potential exposure to a confirmed EHM case.

3. Suspect EHV-1 Horses: An exposed horse that shows no neurologic signs, but displays 

some of the clinical signs consistent with EHV-1 infection; these may include fever (rectal 

temperature greater than 101.5 degrees F), limb edema, abortion, or nasal discharge 

during the 14 days after initial exposure to a confirmed EHM case. Testing of these horses 

is recommended but not necessary as long as the index EHM case has been confirmed. 

Horses not tested will remain suspects and should NOT be included in the confirmed case 

count.

4. Testing of Non-clinical EHV-1 Horses: A decision to test these horses for disease 

investigation or quarantine release purposes must be carefully considered. Non-clinical 

horses can be shedders of EHV-1 virus. Specific recommendations regarding the risk these 

horses pose is lacking in the scientific literature. If performed, a planned response to testpositive non-clinical horses should be established prior to testing such horses.

NOTE: There is no indication to test horses not epidemiologically linked to the disease 

investigation or generally as a part of the quarantine procedure.
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Factors Impacting Decision to Test Exposed Horses

NOTE: If tests are planned, a plan of how to handle the test results must be determined in 

advance.

1. Testing of exposed horses may not be required by regulatory officials if:

a. There is an ability to mitigate further exposure risk by immediate removal of the 

EHM horse or adequate isolation and biosecurity practices of the EHM horse from 

all other horses on the premises;

b. There are no additional clinical cases detected during the 21 day period after initial 

exposure to the index EHM case. Thus, no evidence of disease transmission; and,

c. Epidemiologic investigation provides confidence in owner/ management 

monitoring of the situation through demonstration of twice daily body temperature 

logs, daily clinical assessments, and observance of strict isolation protocols for sick 

horses for the duration of the quarantine.

2. Testing of exposed horses may be required by regulatory officials if:

a. Premises management fails to adequately isolate the index EHM case within 12 

hours of detection. This will result in continued exposure risk to horses on the 

premises;

-ORb. There are exposed horses on premises without adequate isolation from clinical 

horses. Testing may be necessary to determine disease risk;

 -ORc. Epidemiologic investigation reveals evidence of poor compliance including but not 

limited to lack of twice daily body temperature monitoring of potentially exposed 

horses, failure to isolate sick horses, and/or continued sharing of equipment 

between sick and other horses.

 -ORd. SAHO determines that testing of the non-clinical animal is necessary for disease 

investigation and/or mitigation. 

 -ORe. Management elects to reduce quarantine period to 14 days. 
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EHV-1 PCR Test Interpretation of a Clinical Horse*

NOTE: A positive PCR test on a nasopharyngeal/nasal swab sample does NOT necessarily equate 

to presence of infective virus.

• A positive EHV-1 result from a buffy coat sample indicates viremia and an active infection.

• A negative EHV-1 test result on a buffy coat sample indicates the absence of detectable 

EHV-1 viremia at the time of sampling.

• A positive EHV-1 test result from a nasal swab sample should be interpreted as detection 

of EHV-1 DNA in the nasal secretions. EHV-1 DNA can be detected during and subsequent 

to the period of shedding infective virus. Quantitative PCR (i.e. real-time PCR) may provide 

more information about the risk of virus transmission by the sampled horse.

• A negative EHV-1 test result on a nasal swab indicates the absence of detectable virus 

shedding at the time of sampling; provided appropriate sample collection, sample handling 

prior to shipment and sample shipping protocols were followed.

*Interpretation of the PCR test in the non-clinical animal is similar to the clinical animal, however 

the implications of the transmission risk is unknown at this time.

Recommended Protocols for Sample Collection

These are current recommendations:

1. Make contact with the laboratory where samples are to be submitted to obtain supplies

(swabs and transport medium) and laboratory specific sampling and shipping protocols.

2. Be sure to avoid cross contamination by wearing a new pair of examination gloves to collect

samples from each horse and perform hand hygiene between horses sampled. Barrier

precautions such as wearing disposable gown or coveralls and boot/shoe covers should be

observed. These should be changed when sampling horses of different disease status e.g.

clinical cases versus potentially exposed horses.

3. If a chain over the nose or a twitch is used to restrain a horse, it must be washed and

disinfected between horses.

4. A dedicated halter and lead should be used for each horse or these items washed and 

disinfected between individual animals.

5. Nasal swabs should be collected using Dacron tipped swab (Synthetic) with plastic shaft

(Don’t use wooden shaft or cotton tipped swabs)

6. Insert the swab at least 5 inches into the nasal passage and leave swab against the nasal

mucosa for a minimum of 15 seconds before withdrawal.

7. Remove and place swab in a sterile tube (no anticoagulant or gel) or preferably in a tube with

viral transport medium. To prevent over-dilution of the sample less than 2 ml of transport

fluid should be utilized. Label sample according to laboratory instructions.

8. Collect 10ml of whole blood in EDTA (purple top tube) and label sample with animal

name and date and time of collection. Do not send serum for PCR testing.

9. Keep samples cool (refrigerator/ice pack) but not frozen and ship nasal swabs and whole

blood samples overnight to laboratory.

10. Consider direct communication with the laboratory to expedite obtaining results in the most 

timely manner. 
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QUARANTINE PLACEMENT

Overview

There is no universal quarantine protocol that can be applied to all EHM incidents as there are 

multiple factors that must be considered when determining the optimal disease containment 

response. A disease transmission risk assessment is the critical first step in determining the extent 

of a quarantine. Once EHM is confirmed, in those states with quarantine authority, a quarantine 

should be applied in all situations. Additionally, risk assessment identifies specific factors that will 

need to be addressed in establishing the quarantine(s) parameters and required biosecurity 

measures on operations with exposed horses.

In preparation for a disease incident, any equine event or large equine facility should identify an 

appropriate isolation area(s) for clinical and /or exposed animals. Isolation areas on site and off site 

should be identified in advance, including medical facilities with appropriate isolation areas where 

clinical cases could be referred for medical treatment. It cannot be overstated the importance of 

this preplanning preparation.

In dealing with EHM incidents, state animal health officials may issue quarantines to prevent the 

spread of the disease agent, specifically EHV- 1. Science- based criteria for quarantine protocols 

adapted to the specific incident, control disease spread while increasing compliance and minimizing 

the impact on equine movement. Historically, quarantine issuance is by the state veterinary 

authority or horse racing boards. However, in some EHM incidents voluntary quarantine actions are 

taken by private farms, public or private facilities, veterinary teaching hospitals and private 

practitioners for the purpose of controlling the disease. 

Some states have the authority to place “hold” or “stop movement” orders which may be imposed 

while gathering epidemiological data to determine the necessity and proper placement of a 

quarantine.

Before implementing a quarantine, the criteria for quarantine release need to be established. To 

ensure compliance and to determine the effectiveness of disease control measures, the quarantineissuing authority should arrange for a regulatory official or their designee to monitor the situation 

through periodic on-site visits to the premises. Disease transmission, as evidenced by newly 

identified clinical cases, would warrant modification of the quarantine-site biosecurity protocols. 

Additionally, if spread occurs beyond the initial quarantine sites, then additional regulatory 

authorities may need to be contacted and the quarantine may need to be extended or applied to 

additional sites.
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Impact of Quarantine on the Equine Industry

Compliance and cooperation from individuals and the equine industry is essential if EHM is to be 

successfully controlled. The potential impact of any quarantine on the equine industry or individuals 

needs to be balanced with the goal of disease containment. Business continuity must be taken into 

consideration to ensure the equine industry can be supported through an EHM incident. Issuance of 

an extended quarantine period on multiple premises with a low risk of disease development may be 

considered an excessive burden and may be unnecessary for effective disease containment.

Situational awareness and science-based disease prevention guidance from animal health officials 

will garner increased confidence among industry stakeholders and will serve to increase compliance 

and implementation of voluntary disease control measures.

Issuance of a Quarantine

The scope of any premises based quarantine that is to be implemented should be based on the 

results of the risk assessment following the identification of a suspect or confirmed index EHM 

case(s). It may include any of the following scenarios: 

1) Only the suspect index or confirmed index EHM horse is quarantined; 

2) The suspect index or confirmed index EHM horse and horses with high risk of exposure on index 

EHM premises are quarantined; 

3) All horses on the EHM index premises are quarantined; 

4) Entire index premises and horses with high risk of exposure that are located on other than the 

index premises are quarantined; and 

5) An epidemiologically linked non-clinical test positive case is quarantined. 

EHV-1 Risk Assessment for Purposes of Determining Scope of Quarantine

EHV-1 is spread by direct horse to horse contact as well as indirectly by virus-contaminated fomites 

and personnel. The most common route of exposure is through the respiratory tract via aerosolized 

droplets from the respiratory tract secretions of a virus shedding horse.

Infection can also occur by oral or nasal exposure to virus contaminated surfaces. Examples include 

hands, clothing, and equipment such as wipe rags, buckets, water sources, feeders, stall surfaces 

and tack. Clinically affected horses should be assumed to be contagious, particularly with respect to 

respiratory secretions, for at least 14 days. Aborted fetuses, fetal membranes, and placental fluids 

also contain large quantities of infective virus and thus pose a particularly high disease transmission 

risk.
IDOHC EHM Incident Guidance Document 20

Revised January 2018

An assessment is critical in order to identify current disease agent transmission risk factors on an 

affected premises. Identifying the risks for disease agent transmission can assist in determining the 

required quarantine protocols.

1. STEP 1: Assessment of Risk Associated with the Index EHM Case: At the time of the initial 

testing, the contagious nature of the index EHM horse should be evaluated in terms of 

potential for shedding EHV-1 and potential spread of virus from this horse to other horses 

(exposure risk to other horses).

a. Potential to Shed EHV-1: A PCR test result from a horse’s nasopharyngeal/nasal 

swab that the laboratory indicates correlates with a high viral load categorizes that 

horse as a high risk for transmission of EHV-1 to other horses. A clinical EHV- 1 or 

EHM horse with this finding would pose a significant risk of virus shedding into the 

environment.

b. Assessment of the Potential of an EHM Horse to Expose Other Horses: A clinical 

EHV-1 or EHM case which remains on the premises poses significant risk of 

exposure to other equids on the property as it continues to shed virus. A clinical 

EHM horse that is euthanized, appropriately removed, or isolated at onset of 

neurologic signs represents less disease exposure risk to the herd as the source of 

virus has been removed. Appropriate isolation includes restricted access to other 

horses (a minimum of 30 feet, recognizing the distance may need to be greater 

depending upon ventilation, air movement, barn/stall design and other biosecurity 

factors), avoiding the sharing of equipment and/or personnel and utilization of 

protective barrier precautions. A clinical EHM case that is down and thrashing in a 

stall poses a significant virus transmission risk as it requires additional personnel for 

its management compared to a non-neurologic horse and has the potential for 

hyperventilation; all of which may result in a potentially higher risk of 

contamination of the environment. Direct or indirect contact between horses, 

treatment personnel or fomites increases the potential exposure of other horses to 

EHV-1.

A Quarantine Risk Assessment Chart assists in determining level of risk posed by the 

index case (See Appendix). A quarantine restricted to the index horse may be 

sufficient, if the index horse poses a low risk of viral shedding and/or is 

appropriately isolated from other horses on the premises. A more extensive 

premises level quarantine may be warranted if the index horse demonstrates a high 

level of viral shedding and has extensive direct and/or indirect contact with other

horses on the Index EHM premises.
IDOHC EHM Incident Guidance Document 21

Revised January 2018

2. STEP 2: Assessment of Exposure Risk within the Herd: At the time of initial confirmation 

of the index EHM case, the rest of the herd should be classified according to the degree of 

exposure and their ability to transmit virus within the herd. Animals exposed to a large 

amount of the virus are more likely to succumb to infection and/or pose a transmission 

risk to other horses on the premises. These higher risk animals may warrant quarantine 

and monitoring for fever or other clinical signs consistent with EHV-1 infection.

a. Degree of Exposure to EHM Case: An exposed horse is one which is likely to have 

had direct or indirect contact with an EHM case (this includes shared transport 

exposure) within the previous 14 days. Highest risk animals are those with direct 

nose to nose contact with the EHM case during the peak shedding period which is 

defined as the 7-day period before or after the onset of clinical signs. Moderate risk

horses are those sharing a common air space of the clinical case or those, 

equipment, or personnel with direct contact with the EHM case. Animals on the 

premises with limited indirect or direct exposure to the index horse would be 

considered a low/negligible risk for exposure and may not warrant any quarantine 

action. Determining the level of exposure assists in deciding the scope of the 

quarantine to be applied. (See Appendix: Exposure Risk Assessment)

b. Degree of Biosecurity in Place Prior to and at Time of Detection of Index Case: 

Disease risk cannot be completely eliminated at most equine premises, as equine 

premises are seldom managed as a closed facility. An evaluation of current 

management practices will help identify potential biosecurity risks to be addressed 

in the quarantine. Areas to be evaluated include management practices, horse 

stalls, isolation area, wash stalls, commingling areas, equipment handling, transport 

vehicles, and hay and other feed storage facilities. Premises with minimal 

biosecurity protocols in place are more likely to have disease transmission and thus 

warrant a more restrictive quarantine than a premises with a high level of 

biosecurity practices. The degree and level of commonly practiced/everyday 

biosecurity measures will significantly impact disease exposure risk on any given 

premises. Movement of personnel such as veterinarians, farriers, visitors, feed and 

bedding deliverers, and stall cleaners between areas where horses are housed 

constitute a potential risk of disease agent transmission. Therefore, the potential 

spread of EHV-1 due to these movements should be evaluated. A Biosecurity Risk 

Assessment determines the level of risk posed by current biosecurity practices on 

the premises. (See Appendix: Sample Assessment Form) 

Link to AAEP Biosecurity Guidelines: https://aaep.org/guidelines/infectious-disease-control
IDOHC EHM Incident Guidance Document 22

Revised January 2018

c. Degree of Disease Agent Transmission: As the disease incident progresses, the 

situation should be evaluated to determine the level of disease agent transmission. 

Exposed horses on the premises may succumb to disease and present an additional 

disease transmission risk. Evaluate subsequent cases to determine potential time of 

exposure. Modify existing quarantine protocols if disease spread is evidenced by 

new cases with clinical disease after quarantine placement.

d. Assessment of Transmission via Testing at Onset of Investigation: There is a lack 

of consensus among regulatory veterinarians on the appropriateness of testing 

non-clinical exposed horses in an EHM incident. If testing of exposed non-clinical 

horses is being considered, then the response to a positive test result should be 

decided before initiating the testing. Non-clinical EHV-1 infected horses based on 

nasal swab and/or buffy coat testing, currently represent a non- quantifiable but 

potential risk of transmitting virus to horses to which they are exposed. As a 

precaution to minimize the risk of virus spread in any given EHM incident, nonclinical exposed EHV-1 test positive horses should be isolated from non-clinical test 

negative and untested exposed horses. 
IDOHC EHM Incident Guidance Document 23

Revised January 2018

QUARANTINE RELEASE

Overview

During Equine Herpesvirus Myeloencephalopathy (EHM) incidents, the quarantine issuing authority 

(typically the state animal health officials or horse racing authority) issue quarantines and 

subsequent releases to help prevent the spread of EHV-1. However, in some EHM incidents, 

voluntary quarantine actions are taken by private farms, public or private entities, veterinary 

teaching hospitals, horse racing authorities or private practitioners. Criteria for implementing a 

quarantine and for quarantine release should be established and each incident assessed based on 

predetermined guidelines. It must be emphasized that there is no single quarantine release 

protocol that is applicable to all EHM incidents. When striving for optimal disease containment, 

multiple factors must be considered based on the risk assessment performed when placing the 

quarantine.

Clinically affected horses should be assumed to be contagious, particularly via the respiratory route, 

for at least 14 days. Minimal monitoring or quarantine of exposed horses should be for a minimum 

of 14 days after removal and isolation of the EHM horse. Quarantines can be amended to release 

subpopulations of animals earlier if epidemiologic investigation, biosecurity assessment and/or, the 

results of diagnostic testing deem the risk is minimal from the release of a horse or group of horses.

Assessment of the level of clinical disease and the potential for disease spread on the premises is 

critical in determining whether quarantine release is warranted. Release of the quarantine can be 

based on the clinical disease status of the horses on the premises and on the outcome of diagnostic 

testing.

21 Day Quarantine Release without Testing

Release of quarantine shall be based on limiting the potential for spread of the disease agent. 

Immediate removal or appropriate isolation of EHM case(s) decreases the risk of virus transmission 

and spread within the population at potential risk of exposure. Appropriate isolation includes 

restricted access to other horses (a minimum of 30 feet, recognizing it may be greater depending 

upon ventilation, air movement, barn/stall design and other biosecurity factors), avoiding the 

sharing of equipment or personnel and utilization of protective barrier precautions. Diagnostic 

testing of nasopharyngeal/nasal swabs can help provide evidence of the risk of disease spread 

within an exposed population. However, financial constraints and the challenges of scientifically 

based interpretation of risk when dealing with a test positive non-clinical horses limit the benefits 

of diagnostic testing. Accordingly, quarantine release without testing can be an option and is based 

on the clinical disease status on the premises. Any additional horses developing clinical signs 

compatible with EHV-1 infection and diagnosed within the 14 days post strict isolation or removal 
IDOHC EHM Incident Guidance Document 24

Revised January 2018

of an EHM case may be indicative of disease spread on the premises. Strict isolation of EHV-1

clinical cases must include absolutely no horse to horse contact, no sharing of any equipment, strict 

adherence to footwear disinfection at entry/exit to stabling area and use of disposable coveralls 

and gloves.

Quarantine release is recommended, if adequate biosecurity and monitoring has been maintained 

and if no new clinical cases (EHM or EHV-1 cases) are identified in the 21 days from the date of 

removal of the EHM case(s) or 21 days from the resolution of the last febrile case placed in isolation 

or the 21 days from the onset of clinical signs in the last neurologic horse placed in isolation on the

premises. Monitoring of the exposed population for any clinical signs compatible with EHV-1 

infection includes twice daily temperature monitoring and direct observation for compatible clinical 

signs. Any horses subsequently displaying compatible clinical signs of EHV-1 infection including but 

not limited to fever should be immediately isolated and it should be assumed this is a new EHV-1

case, unless diagnostic testing rules out EHV-1 infection and another non-contagious cause of fever 

is found the countdown clock for quarantine release should begin again at 21 days.

Note, a 14 day quarantine release for exposed horses may be considered when there is immediate 

removal (within 12 hours) of the index EHM case and there is evidence of limited potential for 

disease agent spread due to adequate biosecurity and monitoring of horses.

Quarantine Release with Testing

Testing of clinical horses for release of quarantine may shorten the quarantine period. Testing only 

reflects the status of an individual horse on the day of sampling. Positive results could reflect 

reactivation of latent infection or recent exposure. A positive EHV-1 test results warrants further 

investigation to determine if further virus spread is occurring on a premises. If virus spread is 

evident, the quarantine should remain in place. Negative test results from nasal swab and buffy 

coat samples may warrant release of the quarantine. Exposed and clinical horses may be tested 14-

21 days from the resolution of the last febrile case or from the onset of signs in the last neurologic 

horse in assessing the infection status of a premises.

There is a lack of consensus among regulatory veterinarians on the appropriateness of testing 

exposed non-clinical horses. The interpretation of such results based on existing scientific risk 

assessments is problematic. This is because the non-clinical horses that tests positive for EHV-1 on 

nasopharyngeal swab and/or buffy coat, currently represents a non-quantifiable but potential risk 

of transmitting virus to other horses to which it is exposed.

As a precaution and to minimize the risk of disease spread in any given EHM incident, any EHV-1 

test positive horse should be isolated from test negative and non-clinical exposed horses.
IDOHC EHM Incident Guidance Document 25

Revised January 2018

Utilization of Testing Results for Quarantine Modification or Release

1. Testing of Confirmed EHV-1 Clinical Horses: A confirmed EHM case or EHV-1 case with two 

subsequent PCR negative nasal swab and/or buffy coat samples obtained 7 days apart is 

considered to pose a minimal disease transmission risk, thus quarantine release is 

recommended. Note, a minimum of 14 days under quarantine is recommended.

2. Testing of Exposed Non- Clinical Horses: There is a lack of consensus among regulatory 

veterinarians on the appropriateness of testing these non-clinical exposed horses. Testing of 

exposed horses 14 to 21 days from the resolution of the last febrile case or from the onset 

of the last neurologic signs in a horse may be utilized to assess infection status among 

horses on the premises. Any virus positive horse(s) should be promptly removed from the 

group and isolated until confirmed negative on nasal swab and buffy coat PCR testing, or in 

the absence of testing, an adequate period in quarantine before release. As for the 

remaining animals in the exposed group, the clock has to be reset in terms of the period 

they are held in quarantine since one or more of them may have been exposed to the virus 

and may become a shedder.
IDOHC EHM Incident Guidance Document 26

Revised January 2018

EHM INVESTIGATION GUIDELINES

Introduction

In preparation for an EHM investigation, review the biosecurity and diagnostic testing 

recommendations in previous sections of this document. 

When conducting an EHM incident investigation it is helpful to first identify the five “W’s”: which, 

what, where, when, and why? 

• Which is the suspect EHM horse? The age, breed, use, EHV-1 vaccination status and clinical 

signs are important details to record. 

• What is the clinical presentation, the status of the diagnostic testing and physical 

examination? What is the disease agent? The diagnostic test results are essential in 

confirming an EHM diagnosis and determining the case designation category. 

• Where is the EHM horse currently located and where has it recently been? The location of 

the index horse at time of diagnosis and all locations of the index horse for the two weeks 

prior to onset of clinical signs are critical components to the investigation. 

• When did the initial clinical sign(s) appear? Determination of disease onset or exposure date 

is critical to evaluating risks to exposed horses. 

• Why did this/these horse(s) succumb to the disease? Researchers are trying to determine 

why some horses become neurologic while others exposed to EHV-1 don’t. Thus the 

epidemiologic investigation and data collection for all confirmed cases is critical. 

Once the basic information on the index horse or the affected animals is obtained, the objective of 

the investigation is to identify the disease transmission risk factors on the premises, so that they 

can be targeted in any control and prevention plan. The most common transmission route is via the 

respiratory tract by aerosolized droplets of respiratory secretions. Infection is spread by direct 

horse-to-horse contact, as well as indirectly by contaminated surfaces or objects including 

personnel. Environmental transmission of the disease agent of primary concern during an outbreak 

can occur especially when horses are kept in close confinement. Environmental persistence of the 

EHV-1 virus is estimated to be less than 7 days under most conditions with a maximum 

environmental survival of 30 days. Once the EHM incident investigation identifies the risk factors 

for exposure, control measures must be implemented to 1.) Limit the extent of spread and possibly, 

severity of clinical disease on the premises and 2.) Limit the spread of disease to adjacent or 

exposed premises. (See Appendix: EHM Case Investigation Form and Exposed/Trace Horse 

Investigation Form.)
IDOHC EHM Incident Guidance Document 27

Revised January 2018

Outline of Investigator Responsibilities

Use laboratory testing to confirm diagnosis and when reporting on the investigation use case 

definitions to clearly communicate the status of the horses being investigated. 

1. Conduct a case investigation to identify likely source of infection and potentially exposed 

horses. 

2. Utilize case investigation form to document details about the index case and potential for 

exposed horses. 

3. Utilize quarantine risk assessment to identify premises risk factors. 

4. Utilize exposure risk assessment to classify individual horse exposure risk. 

5. Utilize premises biosecurity assessment to identify biosecurity risks to be addressed in 

quarantine. 

6. Be knowledgeable of relevant local, state or other authority jurisdictions and any reporting 

obligations. 

7. Initiate control and prevention measures based on assessment to prevent spread of disease 

agent. 

8. Provide general biosecurity recommendations to the exposed and quarantined premises. 

9. Complete and report all information to appropriate authorities or designated points of 

contact for the incident (where should the report(s) be sent). 

10. Identify and investigate trace-outs and trace-ins of exposed horses to determine appropriate 

regulatory action. 

11. As appropriate, serve as a source for further information: distribute disease fact sheets to 

educate individuals or groups, refer to appropriate other resources or authorities. 
IDOHC EHM Incident Guidance Document 28

Revised January 2018

GENERAL BIOSECURITY RECOMMENDATIONS FOR EHM EXPOSED AND 

QUARANTINED PREMISES

1. Isolate any clinical cases as soon as they are identified

a. Isolation is critical to controlling disease. Ideally, at the onset of suspicion of a 

compatible clinical sign of EHV -1 infection, isolate the affected horse a minimum of 30 

feet from all other horses and potentially further depending on multiple factors 

previously described in these guidelines. Appropriate diagnostics should be utilized to 

determine cause of compatible clinical signs. (For sample collection and diagnostics 

selection see Diagnostic Testing section of this document)

b. Restrict contact with horses to those designated personnel. If possible, assign specific 

personnel to work on positive or suspect cases. Ideally, these designated individuals 

should not handle any other horses on the property.

c. Place a footwear disinfectant station and hand sanitizer outside each isolation stall. 

Provide disposable gloves for designated personnel to wear when handling EHV-1 test 

positive or suspect EHV-1/EHM horses.

d. Restrict access to the isolation area to essential personnel and the isolated animals.

e. Handle isolated horses last; personnel handling isolated horses should not be handling 

other horses without changing clothes. Provide disposable coveralls for use if a change 

of clothes is not feasible when entering and exiting the isolation area.

f. Clean and disinfect the stabling area where the EHV-1 test positive or suspect EHV1/EHM horse has been.

2. Quarantine

a. Quarantine of the premises means that there should be no horse movement on or off 

the premises.

b. Post signage regarding quarantine and biosecurity measures in common areas, such as 

on the notice board outside the office, near restrooms and at entry areas to each barn.

c. Communicate the current quarantine situation to all horse owners and trainers at the 

facility.

d. Limit premises access to essential personnel and vehicles and monitor perimeter of the 

premises for non-authorized entries.

3. Monitor all horses on premises

a. Obtain and record the body temperatures of all horses on the premises twice daily. 

Ideally obtain horse’s body temperature first thing in the morning and last thing in the 

evening and before administering medications which may decrease the body 

temperature.
IDOHC EHM Incident Guidance Document 29

Revised January 2018

b. Report a fever (any temperature of 101.5°F or greater) to a veterinarian for follow up 

collection of nasopharyngeal/nasal swabs and blood to test for EHV-1.

c. Monitor all horses for clinical signs compatible with EHV-1 infection, which include 

ocular or nasal discharge, limb edema, abortion and neurologic signs such as unsteady 

gait, weakness, urine dribbling, lack of tail tone and recumbency. Report the observation 

of any of these signs to the veterinarian designated for follow up collection of 

nasopharyngeal/nasal swabs and blood sampling to test for EHV-1.

4. Restrict human, pet and vehicle traffic from exposed-horse areas

a. Restrict personnel access to only those necessary for the care of the exposed horses.

b. Do not permit dogs in horse areas. Dogs have the potential to carry the virus from one 

area to another on their body.

c. Restrict vehicle traffic including feed/supply delivery vehicles, from entering horse 

stabling areas. Designate an area where vehicles should be parked away from the stable 

area.

d. For extended quarantine situations, farriers and other service provider personnel should 

take appropriate biosecurity measures as outlined in this section to reduce risk of 

spreading the virus.

5. Limit direct horse-to-horse contact

a. Limit potential horse contact in common areas, such as wash stalls, aisle ways and 

arenas.

b. Limit potential horse-to-horse contact when possible by closing upper stall doors or 

installing a physical barrier to restrict horses from extending their heads into the aisle 

ways.

6. Limit stress to horses

a. An EHV-1 exposed horse may potentially be incubating the virus. With stress, an exposed 

horse has a higher likelihood of developing clinical disease and shedding a significant 

amount of virus from the respiratory tract.

b. Any decision regarding management of exposed horses should balance the need to 

contain the disease agent spread with the stress that would occur based on 

management imposed on exposed horses. For example, at race tracks exercise of 

exposed but non-clinical horses is allowed after all other horses have trained and been 

removed from the track since regular exercise of race horses is very important to their 

wellbeing.
IDOHC EHM Incident Guidance Document 30

Revised January 2018

7. Eliminate sharing of equipment and personnel

a. Clean and disinfect all brushes, halters, cross ties, lead ropes and tack which have 

previously been shared.

b. Avoid use of common halters, cross ties, lead ropes, wipe rags, sponges and tack. Use 

individual equipment for each horse; avoid sharing equipment.

c. If equipment must be shared, clean and disinfect all equipment before and after each 

use. This includes feed buckets and other feeding and stall cleaning utensils.

d. Avoid tying horses to fences or tie rails.

e. Avoid possible viral contamination of water buckets by not allowing the hose to enter or 

contact the bucket when filling the bucket with water.

f. Designate traffic pattern for wheeled vehicles (i.e. tractors, gators, wheelbarrow etc.) 

used for handling hay, feed, shavings or supplies to limit disease spread.

8. Clean and Disinfect

a. Clean all barn, other stabling, trailer, or other equine contact surfaces thoroughly, 

removing all organic matter (dirt, nasal secretions, uneaten feed, manure, etc.) before 

applying a disinfectant. It is important to remember that organic material decreases the 

effectiveness of the disinfectant, especially if 10% bleach is used as the disinfectant.

b. Clean all shared equipment and shared areas to remove dirt and manure before 

application of a disinfectant. 

c. Completely clean and disinfect the stall surfaces of the known-infected horse and any 

equipment and objects that may be contaminated. Properly dispose of potentially 

contaminated materials generated by the cleaning and disinfection process.

9. Use footwear disinfectant, hand sanitizer 

a. Place footwear disinfection stations and hand sanitizers at other strategic locations, 

throughout the barn areas and encourage their use.

b. Encourage regular cleaning of footwear disinfection stations and ensure use of 

footwear disinfection stations upon entry and exit of infected animal stalls.

c. Routinely clean footwear disinfection stations to avoid buildup of organic material, 

such as dirt and manure, which may inactivate the disinfectant.

d. Assign a person to monitor the footwear disinfection station and promptly clean and 

replenish the disinfectant as needed.
IDOHC EHM Incident Guidance Document 31

Revised January 2018

10. Use of Personal Protective Equipment (PPE) for Isolated Horses (an excellent training module 

on PPE for veterinarians can be accessed at the following link—module #10): 

https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/nvap/ct_aast

a. Assign a person knowledgeable on infection disease protocols to oversee isolated sick 

horse stabling. This person shall ensure proper donning and doffing of PPE. 

b. Reusable coveralls should be clean upon entry into isolated stabling and should be used 

for a single designated animal. Re-use of coveralls should be permitted provided there is 

limited contamination of outer surface. 

c. Disposable coveralls should only be used for handling one infected horse and can be reused provided they have limited amount of contamination and are stored in a manner to 

prevent virus spread. 

d. Coveralls being reused should be stored properly to limit contamination and transfer of 

virus. 

e. Disposable coveralls should be dedicated to one individual and not shared amongst 

personnel. 

f. Outerwear should be donned in a manner which prevents contamination of inner or 

outer surfaces. Ideally, outwear should be donned in a clean dry ground surface (i.e.

pavement).

g. Excessively soiled or ripped disposable coveralls should be properly disposed to limit 

virus spread. 

h. For specifics regarding PPE supplies, please see attached chart on the following page.

11. Bedding from isolated horses. Soiled bedding can contain infectious virus.

a. Dedicated cleaning equipment should be maintained for each stall/horse.

b. Disposal of soiled bedding should be handled in such a manner as to limit 

access/exposure to other horses, barns and structures on the premises.

NOTE:

Isolation of all mules away from horses may be an important strategy in EHV-1 disease control 

during an EHM incident. Recent scientific studies have investigated the role of mules as silent 

shedders of EHV-1 during an EHM incident. During a 2011 EHV-1 disease investigation involving 

mules and horses in California, high viral nasal shedding and viremia was detected in some of the 

asymptomatic mules. It is important to note that the detection of EHV-1 in asymptomatic mule 

samples indicates their susceptibility to infection and their potential role in virus spread.
IDOHC EHM Incident Guidance Document 32

Revised January 2018

Personal Protective Equipment (PPE) Supplies

Product 

Name/Type

Potential Source Contact Info Approximate 

Cost

Plastic aprons Grainger (800) 472-4643 www.grainger.com $199.20 per 

package of 100

Tyvek coverall with 

attached hood, 

elastic wrists and 

ankles

Enviro Safety 

Products, Valencia, 

CA 91355

(800) 637-6606 Fax: (559) 746-

0317 www.envirosafetyproducts.com

$114.99 per 

package of 25

White disposable 

gowns

eSafety 

Supplies Ci

ty of Industry, CA 

91746

(877) 693-3754 (626) 369-

1280 www.esafetysupplies.co

m

$30.03 per 

package of 50

Disposable plastic 

boots ("Knot-aBoot")

QC 

Supply 

 Schuyler, NE 68661 

(800) 433-6340 (402) 352-

3167 www.qcsupply.com

$14.99 per box of 

50

Virkon-S - use 

spray bottle for 

disinfection of 

soles of 

boots/shoes

Valley 

Vet 

Marysville, KS 66508

(800) 419-9524 Fax: (800) 446-

5597 www.valleyvet.com

$70.95 per 10 lb 

container

Alcohol hand 

sanitizer- use 

product with at 

least 61% alcohol

Multiple 

sources Exampl

es include Purell and 

3M Avagard

www.purell.com www.3m.com Purell: ~$1 per 2 

oz bottle; 3M 

Avagard: $13.50 

per 16 oz bottle

Single-use 

thermometer 

probe covers

Valley 

Vet 

Marysville, KS 66508

(800) 419-9524 Fax: (800) 446-

5597 www.valleyvet.com

$2.49 per 

package of 30

Water and feed 

buckets 

Valley 

Vet 

Marysville, KS 66508

(800) 419-9524 Fax: (800) 446-

5597 www.valleyvet.com

~$4.49 per 

bucket 

Disinfectable 

Halter and Lead

Valley 

Vet 

Marysville, KS 66508

(800) 419-9524 Fax: (800) 446-

5597 www.valleyvet.com

$19.95 for halter 

and $7.49 for 

lead

Disinfectable 

Grooming Brush 

Set 

Valley 

Vet 

Marysville, KS 66508

(800) 419-9524 Fax: (800) 446-

5597 www.valleyvet.com

6.95 per brush 

set
IDOHC EHM Incident Guidance Document 33

Revised January 2018

EHM INCIDENT COMMUNICATION 

Overview

Equine Herpesvirus- 1 neurologic disease or equine herpesvirus myeloencephalopathy (EHM) is a 

topic about which a great deal of information/misinformation continues to be posted on websites, 

blogs, Facebook postings, Twitter and Instagram. With the increasing popularity of social media, the 

need for timely and accurate communication during any EHV-1 incident is critical. Stakeholders 

have recognized the need for accurate, clear, consistent information in order to make well informed 

decisions about equine health management. When factual information is lacking, misinformation 

can spread quickly creating unnecessary anxiety among equine owners and others in the industry. 

For successful communications during an EHM incident, media training for individuals involved in 

EHV-1 messaging is strongly recommended. Risk communications training provides insight into the 

key W’s that need to be addressed in disease incident communications.

It is recommended that state animal health officials should establish a communication plan for an 

EHM incident well in advance of the incident. Appropriate contacts with industry, other state 

equine officials and federal resources should be made prior to the event of an incident. Drafting 

content for webpages, alerts and printed outreach materials prior to an incident will facilitate 

timely dissemination of accurate and useful information during the incident. State animal health 

officials should explore all modes of communication and utilize effective resources for 

communicating information.

To Whom to Communicate?

Initial communication during an EHM incident starts with the index premises. To encourage 

cooperation of all parties at the onset of the incident, face-to-face meetings between the facility

owner(s), event manager(s), and horse owners/trainers on facilities with multiple horse owners 

such as boarding facilities or racetracks, practicing veterinarians and the state animal health official 

are highly recommended. Inclusion of the regulatory officials in the communication process helps to 

give the perspective of “we are in it together” for the welfare of the horse and the industry. All 

communication should target those impacted by the EHM incident, such as the individual horse 

owners, whose concern may be centered on how the disease occurrence affects their horse(s) and 

the economic impact from possible animal losses and restrictions on movement.

Once communications have taken place with the responsible person(s) on the index premises, 

information should be more widely disseminated to the equine industry at large to include but not 

limited to contacting the Equine Disease Communication Center (EDCC) 

(www.equinediseasecc.org). 
IDOHC EHM Incident Guidance Document 34

Revised January 2018

(It is important to include information regarding when a quarantine was instituted as well as follow 

up information as to when the quarantine was lifted.)

Delay in communications will allow time for rumors to develop and spread. It is recommended that 

state animal health officials develop a communication network for dissemination of equine disease 

alert information within their states. Some states have successfully used email lists to distribute and 

alert key equine industry representatives and equine practitioners in the state. Those alerted 

should in turn disseminate the information to their respective constituents. An email notification 

system ensures a reliable source is providing a consistent message for the state. In addition to email 

alters, state animal health webpages and social media sites can host the most current factual 

information. States with large event facilities should consider a notification system for event 

facilities including race tracks.

When to Communicate?

Timeliness of communication is critical. However, it is essential to first consider the need to 

communicate the information. For example, a single horse out on pasture that has never left the 

premises and has no potential to expose another horse may not warrant communication to the 

entire equine industry as there is minimal risk outside of the horse’s index premises. However, a 

horse displaying neurologic signs five days after participating at a large national horse show along 

with a history of a fever preceding the development of neurologic signs, that has been confirmed 

positive test for EHV-1, presents a significant risk and warrants widespread dissemination of 

information on the status of the situation.

It is recommended that communications with the industry occur within 24 hours of the initial 

investigation and confirmation of the EHM case. States with experience in communicating EHM 

incidents have cautioned others that communicating about a suspect but not yet confirmed case of 

EHM may be premature as there are many differential diagnoses for a previously febrile horse that 

is now exhibiting neurologic signs. Therefore, it is recommended that only confirmed case 

information be disseminated to the industry. Where a rampant rumor mill situation exists, state 

animal health official action to clearly communicate the status of the situation is necessary. The 

state animal health official may want to acknowledge that an investigation is ongoing but that no 

cases of EHM have as of yet been confirmed and indicate when further information will be made 

available.

What to Communicate?

The key to communication is providing factual information that addresses the concerns of the 

industry. Do not speculate. The outreach to affected premises should include specific biosecurity 

recommendations and quarantine parameters. Owners of all identified exposed horses should be 

provided a temperature monitoring log for tracking twice daily temperatures and any other clinical 

signs.
IDOHC EHM Incident Guidance Document 35

Revised January 2018

There are multiple different stakeholders in equine disease communication. Generally equine 

stakeholders want to know if a particular EHM incident can impact them. For example, the 

individual horse owner is concerned about risk to his/her horse, the show manager is concerned 

about risk to their event, and the equine practitioner is concerned about risk to the health of the 

horses in their practice area. Each individual utilizes the information available to assess risk as it 

pertains to them and their role in an incident. The critical information state animal health official 

can provide to the stakeholders includes: how many horses are affected, the population of horses 

affected, potential exposures, and the measures implemented to limit the disease spread. This 

information can be in the form of social media alerts, webpage updates and printed outreach 

materials. State animal health officials are urged to place information on their department’s 

website. 

State animal health officials, the AAEP and the AHC have developed a plan for a National Equine 

Disease Communication Center to assist dissemination of factual current information at 

www.equinediseasecc.org. The EDCC has been designed to become the central “go-to” source for 

information about equine infectious diseases that pose a threat to the horse industry and the 

website is intended to be a central communication resource for the equine industry to provide 

current, factual information regarding ongoing outbreaks in all fifty states. 

Outlined below are some recommendations for regulators for messaging content for webpages, 

alerts, and social media.

1. Recommended Website Content

a. See Definitions section of guidance document for case definitions to be posted to the 

website.

b. Compatible Clinical Signs: See Definitions Section of Guidance Document

c. Resources:

i. USDA Webpage: 

http://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-diseaseinformation/horse-diseaseinformation/sa_herpes_virus/ct_equine_herpes_virus_type_1

ii. USDA Brochure: 

http://www.aphis.usda.gov/vs/nahss/equine/ehv/equine_herpesviru 

s_brochure_2009.pdf

iii. AAEP Website

1. Resources for Horse Owners: 

https://aaep.org/sites/default/files/Documents/DiseaseFactsheetEHV

.pdf
IDOHC EHM Incident Guidance Document 36

Revised January 2018

https://aaep.org/sites/default/files/Documents/DiseaseFactsheetEH

M.pdf

2. Resources for Veterinarians

a. EHV Control Guidelines: 

https://aaep.org/sites/default/files/Guidelines/EHV1_4_Final.

pdf

b. UC Davis: How to set up an Isolation Unit: 

http://www.vetmed.ucdavis.edu/ceh/docs/IsoUnit061611.pdf

iv. Equine Disease Communication Center (EDCC)

1. www.equinedisease.org

d. Alert about New Cases: Posted Daily

i. Sample Verbiage to Include When Posting on Website: Day one

1. On [X Date], a [X] year old, breed, sex, displaying 

mild/moderate/severe neurologic signs has been confirmed test 

positive for Equine Herpesvirus-1. The test positive horse has been 

quarantined and isolated in [X] County. Exposed horses have been 

quarantined and are being monitored twice daily for fever 

(temperature over 101.5° F) and other clinical signs. An 

epidemiological investigation has been initiated. State animal health 

officials will continue to monitor the situation.

ii. Sample Verbiage To Include when Posting on Website: Subsequent Days

1. No new cases have been detected. Epidemiologic investigation 

reveals no additional exposed horses beyond index premises.

2. An exposed [X] year old, breed, sex, displaying a fever of 101.5°F 

has been confirmed positive for Equine Herpesvirus-1. This horse 

had direct exposure to the index horse and has been isolated. 

Exposed horses continue to be monitored. Epidemiologic 

investigation reveals horses participated in a show at [X] premises 

on [X date]. (After discussion and notification of event 

management.) State animal health officials are contacting owners 

of potential exposed horses. All exposed horses should have 

temperatures taken twice daily and be observed for any clinical 

sign consistent with EHM. Any temperature over 101.5° F or 

compatible clinical signs should be reported to a veterinarian for 

investigation and diagnostic testing.
IDOHC EHM Incident Guidance Document 37

Revised January 2018

3. The test positive horse has been released from quarantine based 

on two negative test results. No additional horses have been 

detected. The investigation has been closed.

e. Historic EHM Incidents

i. Date and County

1. Index case: a [X] year old, breed, sex, displaying 

mild/moderate/severe neurologic signs was euthanized or recovered. 

Laboratory results confirmed Equine Herpesvirus-1. [X] additional 

confirmed cases of EHM and [X] additional febrile horses confirmed 

test positive for EHV-1. All horses are recovering or [X] horses were 

euthanized. No epidemiologic link to any previous incidents. (Graphic 

Map of case premises locations would be helpful if anonymity of 

premises can be maintained).

2. Recommended Incident Specific Outreach Materials

a. Answers to Commonly Asked Questions to include in outreach materials.

i. When did the outbreak begin?

ii. Where can I get the most current information on the outbreak?

iii. Where do I report a suspect case?

iv. What type of horses (use of horses e.g. rodeo, show, race, pleasure etc.) are 

primarily affected?

v. Is my horse at risk?

vi. Has there been spread of the disease?

vii. Are there movement restrictions?

viii. When will updates be available?

b. Outreach for Premises

i. Provide recommended Biosecurity Practices for EHM Premises
IDOHC EHM Incident Guidance Document 38

Revised January 2018

EHV-1 VACCINATION

Overview

Currently available vaccines against EHV-1 provide some protection against the respiratory and 

abortion forms of the disease but fail to protect against EHM. Unfortunately, there is insufficient 

data to make scientifically sound vaccination recommendations. The following summary 

information is offered for your consideration.

During a presentation at the EHV workshop held at USAHA in 2013 

(http://www.usaha.org/upload/Committee/InfectiousHorses/report-hd-2013.pdf, a speaker 

indicated that there is scant scientific evidence of efficacy of any of the available vaccines against 

EHV- 1 neurologic disease. The critical event in the pathology of neurologic disease is endothelial 

vasculitis and thrombosis in the central nervous system. There is little evidence that vaccination 

with any available product prevents or decreases either event. Also mentioned were two peer 

reviewed publications that actually showed there may be an association of recent or frequent 

vaccination of horses against EHV-1 with an increased risk for development of EHM during EHV-1 

outbreaks.

Vaccination of competitive horses with EHV-1 products is common. For example: The USEF 

currently requires horses over 7 months of age to be vaccinated for EHV within six months prior to 

entering the grounds or stable areas of their sanctioned events. A number of racing jurisdictions 

have similar requirements. The current AAEP vaccination guidelines recommend vaccination for 

EHV every 6 months for: animals on facilities with frequent horse movement, show and 

performance horses, racetracks and other high risk environments and horses less than 5 years of 

age.

EHV-1 Vaccination Considerations

Several EHV-1 vaccines currently marketed in North America carry a label claim for the control of 

respiratory disease induced by EHV-1 and EHV-4. These are multi-component inactivated vaccines 

specifically (as of January 2018) Prestige® (Merck), Calvenza®, Vetera (Boehringer Ingelheim 

Vetmedica) and Fluvac Innovator® (Zoetis) and the single antigen modified live vaccine Rhinomune® 

(Boehringer Ingelheim Vetmedica). Additionally, there are two EHV-1 inactivated vaccines licensed 

for the prevention of abortion and respiratory disease; these vaccines are Pneumabort-K® (Zoetis) 

and Prodigy® (Merck). There are currently no EHV-1 vaccines licensed to prevent EHM.
IDOHC EHM Incident Guidance Document 39

Revised January 2018

It has been suggested that some EHV vaccines may assist in limiting the spread of EHV-1 in outbreak 

situations by limiting nasal shedding of EHV-1 and thus dissemination of virus. For this reason, some 

experts hold the opinion that there may be an advantage to vaccinating in the face of an outbreak. 

Based upon the current available literature, the vaccines with the greatest ability to limit nasal 

shedding and viremia of the neuro virulent strain include the vaccines licensed for control of 

abortion (Pneumabort-K® & Prodigy®), the MLV vaccine (Rhinomune®) and another inactivated 

vaccine for prevention of respiratory disease (Calvenza®)

It is recognized that in an outbreak situation, some veterinarians, owners and/or trainers may elect 

to vaccinate horses on the premises. Thoughtful consideration should be given before this activity is 

initiated. If this approach is pursued, it is important to understand the following:

1. There are no EHV-1 vaccines currently licensed to prevent EHM.

2. Only afebrile and asymptomatic horses should be vaccinated and protection against 

clinical EHM should not be an expectation.

3. A certain percent of vaccinated animals will respond with a low grade fever, lethargy 

and/or injection site discomfort for anywhere from 24 -72 hours (or longer) post 

vaccination. These fevers can exceed 101.5° F.

4. Horses with post-vaccination fevers can increase the number of animals meeting 

isolation, monitoring and testing requirements and increase the cost of outbreak 

management.

5. The current/previous vaccination status of each animal should be obtained and 

evaluated as part of this decision process.

6. Vaccination should not be considered a substitute for or equivalent to implementation 

of good biosecurity measures.

For additional vaccination guidance see the American Association of Equine Practitioners EHV-1 

Vaccination Guidance for Private Practitioners at visit https://aaep.org/guidelines/vaccinationguidelines
IDOHC EHM Incident Guidance Document 40

Revised January 2018

APPENDIX

1. Quarantine Risk Assessment

2. Exposure Risk Assessment

3. Premises Biosecurity Risk Assessment

4. Quarantine Release Assessment

5. EHM Case Investigation Form

6. EHV-1 Exposed/Trace Horse Investigation Form

7. Flow Charts
IDOHC EHM Incident Guidance Document 41

Revised January 2018

QUARANTINE RISK ASSESSMENT

Assessment of management practices seven (7) days prior to and subsequent to identification of the index EHM

case.

Level of Isolation of Infected Horses: 

(Any yes answer is considered an increased risk) Yes No

Is it possible for the infected horse to have nose-to-nose contact with other horse(s)?

Can the infected horse place its head into a common alleyway and make physical contact with

humans, equipment or other horses?

Are there openings in the stall sides between the infected horse stall and the stall next to him?

Is the nearest horse stalled closer than 30 feet to infected horse(s)?

Is there a horse in the stall(s) adjacent to the infected horse?

Is there a horse in the stall(s) across the alley from the infected horse?

Is the infected horse turned out into a pasture or paddock which other horses use?

Do the same personnel handle healthy and infected horses?

Is disposal of manure from isolated horse unrestricted?

Are dogs permitted in the stabling areas?

Sharing Equipment or Personnel

(Any yes answer indicates a potential means of EHV-1 spread) Yes No

Does any other horse have access to the infected horse’s water bucket?

Does any other horse have access to the infected horse’s feed bucket?

Does any other horse have access to the infected horse’s halter or other tack?

Does any other horse have access to the infected horse’s grooming equipment?

Does any other horse share crossties with the infected horses?

Does any other horse have access to personnel who have worked directly with the infected horse (to

include but not limited to veterinarian, farrier, feed or delivery personnel and stall cleaners)?

When watering horses, is the end of the hose submerged into the infected horse's water bucket?

When feeding horses, does the common grain scoop make contact with the individual stall feed tubs?

Are the wheeled vehicles (tractors, gators, wheelbarrows) shared for movement of hay, feed, shavings 

and manure?

Protective Equipment 

(Any no answer may lead to increases in disease spread) Yes No

Is a footwear disinfection required every time a person enters and exits an infected horse’s area during 

the quarantine period?

Is there minimal organic material in the footbath?

Are footbaths changed at least daily or more frequently in high traffic areas?

Are boot covers or boot disinfection required when handling infected horse?

Are separate coveralls or clothes required when handling the infected horse?

Are disposable waterproof gloves required when handling infected horse?

Is everyone, including visitors, provided requirements or information regarding the biosecurity

measures in place?

Are coveralls disposed of or laundered after each entry into the infected horse stabling area?
IDOHC EHM Incident Guidance Document 42

Revised January 2018

Exposure Risk Assessment

Exposure Risk: Answers of “Yes” signify increased risk of disease agent spread (Time period for assessment: 7

days prior to diagnosis of EHM and 7 days post diagnosis of EHM case.)

Is the exposed horse showing clinical sign(s) of disease? ___________

Did the exposed horse(s) have direct contact with an infected/ sick horse in the stabling area? ____

Did the exposed horse(s) have direct contact with infected/ sick horse in any common area? ____

Did the exposed horse(s) have direct contact with infected/ sick horse in any exercise area? ____

Did the exposed horse(s) have contact with infected/ sick horse in any pastures or paddocks? ______

Did the exposed horse(s) have contact with equipment used on the infected/sick horse?

Did the exposed horse(s) have contact with people handling/feeding the infected/sick?

Did the exposed horse(s) have contact with infected/ sick horse during shipment to the premises? _______

General Exposure Risk Quarantine Guidelines

Low-Exposure Risk

Horse

No known exposure on index EHM

case premises

Minimal risk; recommend monitoring for

clinical signs.

Medium-Exposure Risk

Horse

Potential exposure on index EHM

case premises

Recommend monitoring body temperature

of horse for 14 days

High-Exposure Risk

Horse

Known direct contact with index

EHM case

Recommend Quarantine and Isolation

Monitoring and testing of any horse which

develops fever or neurologic signs.

(*Note: If testing non-clinical horses, must 

have a plan in advance on how to handle a 

positive result)
IDOHC EHM Incident Guidance Document 43

Revised January 2018

Premises Biosecurity Assessment

 Stalls

Walls Solid Half walls Bars

Material Metal Treated wood (nonporous)

Untreated wood

(porous)

 Isolation Area

Isolation

Location

Available designated

empty barn or

paddock/pen/pasture

isolated away from all

other stalls

One empty barn at the

end of the barns

A few stalls available

at one end of barn

housing horses

Personnel

Access

Isolation personnel

access only

Limited

access

No ability to restrict

access

Vehicle Access

Restricted vehicle

access with

monitoring at

entrance to premises

and isolation stabling

Restricted vehicle

access with

no monitoring of

entrance

No restrictions or

monitoring of

vehicle access

 Feed and Water

Feed storage

Covered hay and

sealed containers for

feed kept in a

separate secure stall

Secure storage stall

with open feed bags

and uncovered hay

Hay and open feed 

bags in uncovered

barn aisle way

Water sources

Only individual water

buckets in use

Stream or large water

Source

Communal water

area

Separation of

Feed and

Manure

Handling

Equipment

Complete separation

of feed and manure

handling equipment

Limited separation of

feed and manure

handling equipment

Feed, hay and

manure handling

equipment stored

together

Minimal

Biosecurity Risk

Medium

Biosecurity Risk

High Biosecurity

Risk

Disease risk cannot be completely eliminated from an equine premises as these premises are

seldom closed to both new arriving horses or equine service providers. An evaluation of

current management practices will help identify potential biosecurity risks which should be

addressed in the quarantine.
IDOHC EHM Incident Guidance Document 44

Revised January 2018

Wash Stall Area

Horse-to-Horse

Contact

No nose-to-nose

contact possible

Limited duration or

frequency of

nose-to-nose contact

possible

Nose-to- nose contact

likely

Equipment No Sharing of

Equipment

Restricted

sharing of equipment

(i.e., horses in same 

barn)

No restrictions -

equipment is freely

shared

Hose Contact

with Horse

Horse never makes

direct contact with

hose

Horse makes limited

direct contact with

hose

Horse has direct

contact with hose

Hose

Placement

Hose is hung

on wall after each use

Hose is sometimes

hung after each use

Hose is

left lying on the

ground

Fecal Material Removed

Immediately

Routinely removed

throughout the day

Removed at the end

of the month.

Horse Commingling Areas

Exercise Area

No shared exercise

areas:

All horses exercise

independently

Shared exercise area

with minimal possible

direct horse-to-horse

contact

Shared exercise area

with

direct horse-to-horse

contact

Pastures/

Paddocks Area

No shared pasture/

paddocks

all horses in

designated individual

pasture/ paddock

Shared pasture/

paddocks

with minimal direct

horse-to-horse contact

Shared pasture/

paddocks with 

direct

horse-to-horse

contact

Parking

Trailer

Feed/Hay/

Shavings Trucks

Restricted trailer

parking, monitored

and separate from

barn area and not

accessible by visitors

Shared parking, but

separate from visitor

access

Unrestricted parking

next to horse barns

and accessible to

visitors

Visitor

Restricted visitor

parking, monitored

and separate from

barn and trailer

parking

Shared parking, but

separate from trailer

parking

Unrestricted Parking

TOTALS

Minimal

Biosecurity Risk

Medium

Biosecurity Risk

High

Biosecurity Risk
IDOHC EHM Incident Guidance Document 45

Revised January 2018

QUARANTINE RELEASE ASSESSMENT

Index EHM Case Information:

Clinical Onset Date:

Date of Isolation or Removal from Premises:

General Quarantine Release Criteria:

Was the EHM case euthanized? □ yes □ no

Was the EHM case adequately isolated within 12 hours of detection of neurologic signs, from

other horses on premises? □ yes □ no

If no should extend quarantine release time.

Quarantine Options (One or more yes responses may warrant quarantine release)

Has it been 21 days since onset date of last EHM case? □ yes □ no

Are there negative test results on exposed horses? □ yes □ no

Evaluation of Infected Premises Status

(If answer no to all questions, quarantine release is recommended at 21 days after last

onset date of clinical signs of the last case.)

Have the horse’s temperatures been monitored since first case of disease was detected?

□ yes □ no

Has a temperature log been maintained? (Review Log) □ yes □ no

Have any exposed horses had a fever (rectal temperature greater than 101.5 F)?

□ yes □ no

Have any exposed horses displayed any clinical signs compatible with EHV-1 infection?

□ yes □ no

Has the EHM case had direct contact with any horses since confirmation of EHM?

□ yes □ no

Testing for Quarantine Release:

(If answer yes to all questions, quarantine release is recommended.)

Were diagnostic samples obtained? □ yes □ no

Were samples obtained 14 days after removal of EHM case or □ yes □ no

21 days after onset date of last EHM case or resolution of last febrile case.

Were negative PCR results obtained for all samples tested? □ yes □ no
IDOHC EHM Incident Guidance Document 46

Revised January 2018

 Equine Herpesvirus Myeloencephalopathy Case Investigation Form

Investigator: Date:

Veterinary Contact Information:

Veterinarian Contact phone 

Clinic name

Owner Information

Last name First name

Address

City State Zip County

Phone Number Email Address

Point of Contact if Different than Owner

Current Horse Location

Address

City State Zip County

Type of Facility □ Private Residence □ Show Grounds □ Racetrack

 □ Boarding Facility □ Training Facility □ Breeding Facility

Premises Information

Barn Manager/ Trainer/ Event Manager Name _ ___________

Contact Phone Number

Contact Email Address

Total Number of Horses on the premises 

Total Number of Barns on the premises

Is there an isolation barn or area on the on the premises? □ yes □ no

Are all horses on premises owned by the same Individual? □ yes □ no

Describe Stall/ Barn Facility: (Panel fencing access to other horses, half boarded walls and bars

access to other horses, stall is at the end with no other horses etc.) (Attach photos or google earth map)
IDOHC EHM Incident Guidance Document 47

Revised January 2018

Positive EHM Case Record

Name: Microchip/Brand:

Breed: Gender: Mare | Stallion | Gelding Age:

Primary Use: 

Level of Exercise at time of confirmation: 

Stabling: □ Stall □ Paddock/Corral □ Pasture

Dates of EHV-1 Vaccination(s): Name of Product Administered: ____

Date of onset of initial clinical sign(s)?

Clinical Signs Observed in Affected Horse: Check all that apply and write date of onset

□ Ataxia ________ □ Colic ________ □ Fever ____ °F ________

□ Flaccid Tail ________ □ Hindend Weakness________ □ Incoordination ________

□ Lethargy ________ □ Limb Edema ________ □ Nasal Discharge ________

□ Recumbent ________ □ Dribbling Urine ________ □ Abortion ________

□ Unable to rise ________ Other: ________________________________________

Was the horse euthanized? □ yes □ no If yes, what date? _______________

Was the horse necropsied? □ yes □ no If yes, where? _______________

Laboratory Results

Laboratory Name: Phone Number:

Date 

Collected

Sample 

Type Type of Test

Strain Type 

Detected Quantitative Result 

Travel History: List all locations where the horse has been the 2 weeks prior to onset of clinical

symptoms?

Date of Travel

Reason For Travel 

( Event Name)

Destination City, 

State Transportation Method

Comments:
IDOHC EHM Incident Guidance Document 48

Revised January 2018

Exposed Horse Information

Total Number of horses with clinical signs consistent with EHV-1:

Total Number of non-clinical EHV-1 test positive horses:

Are temperatures taken twice daily on all horses? □ yes □ no

Have any horses died over the last two weeks? □ yes □ no

If yes, provide number of dead horses and clinical presentation prior to death: _______

Are horses on a routine EHV-1 vaccination plan? □ yes □ no

Date of Last Vaccination: ______________ Product Administered: _______________

Exposed Horses Demographics: (List any potentially exposed horse)

Name Breed Age Sex 

Date Clinical 

Onset 

Fever/ Neuro/ 

None

List any horses which have left the premises over the last two weeks?

Date of 

Departure

Horse’s Name 

& Description

Destination 

Premises Name 

& Contact Name

Destination Contact 

Phone Number 

Destination Premises 

Location

Investigation Comments:

Quarantine Number Issue Date
IDOHC EHM Incident Guidance Document 49

Revised January 2018

 Equine Herpesvirus Myeloencephalopathy Case Investigation Form

Investigator: Date:

Veterinary Contact Information:

Veterinarian Contact phone ___

Clinic name

Owner Information

Last name First name 

Address

City State Zip County

Phone Number Email Address

Point of Contact if Different than Owner

Current Horse Location

Address

City State Zip County

Type of Facility □ Private Residence □ Show Grounds □ Racetrack

□ Boarding Facility □ Training Facility □ Breeding Facility

Premises Information

Barn Manager/ Trainer/ Event Manager Name __________________________________________

Contact Phone Number

Contact Email Address

Total Number of Horses on the premises _________

Total Number of Barns on the premises _________

Is there an isolation barn or area on the on the premises? □ yes □ no

Are all horses on premises owned by the same Individual? □ yes □ no

Describe Stall/ Barn Facility: (Panel fencing access to other horses, half boarded walls and bars access to 

other horses, stall is at the end with no other horses etc.) (Attach photos or google earth map)
IDOHC EHM Incident Guidance Document 50

Revised January 2018

Trace Horse Record

Name Microchip/Brand _____

Breed Gender Mare | Stallion | Gelding Age______

Primary Use 

Level of Exercise at time of confirmation 

Stabling □ Stall □ Paddock/Corral □ Pasture

Dates of EHV-1 Vaccination(s)

Name of Product Administered

Any clinical sign(s)? Check all that apply and write date of onset

□ Ataxia ________ □ Colic ________ □ Fever ____ °F ________

□ Flaccid Tail ________ □ Hind Weakness________ □ Incoordination ________

□ Lethargy ________ □ Limb Edema ________ □ Nasal Discharge ________

□ Recumbent ________ □ Dribbling Urine ________ □ Abortion ________

Other: ____________________________________

Investigation Comments: 

NOTE: If any horses on this property display neurologic signs then the full case epi investigation

shall be completed.
IDOHC EHM Incident Guidance Document 51

Revised January 2018 EHM Suspect (Compatible Clinical Signs)

ISOLATE 

OFFSITE (Optimal)

Euthanize

Sample Collection • Nasal Swab (Synthetic Swab inserted 5 inches into nasal cavity for 

15 seconds) AND 10 ml Whole Blood (EDTA) • Necropsy Tissue Samples

LABORATORY PCR TESTING

Screening Assay: Glycoprotein B gene

Differentiation Assay: DNA Polymerase gene

Positive Result

Blood Positive = Viremia

Nasal Swab Positive= Viral Shedding

Negative Result

If Answer NO to any resample: • Adequate sample 

quality • Appropriate test 

requested • Appropriate timing of 

sample collection • Appropriate Sample 

storage and handling

High 

Risk Low Risk • High Viral Shedding • Index horse not isolated within 12 hours • Index EHM horse within 30 feet of other horses • Routine use of shared equipment without cleaning and 

disinfecting • Poor biosecurity management practices observed during risk 

assessment • Euthanized Index EHM Case • Index EHM case moved offsite within 12 hours • Index EHM case immediately isolated onsite at least 30 

feet away from all other horses • All horses test negative • Limited to no horse to horse contact • High biosecurity standards verified during risk assessment

Quarantine Index EHM Case Only

Quarantine Index and High Risk Exposed Horses 

or Entire Premises

Assessment for 

Quarantine Release (Release Assessment – See appendix) Release with 

Testing

21 day Release 

Without Testing • Exposed and/ or Clinical Horses tested 14-21 days from the 

last febrile/clincial case • Confirmed cases have two negative test results (blood and 

nasal swab) from samples collected at least 7 days apart. • Minimum of 14 days Qurantine Release if the immediate 

removal of index case, all exposed horses onsite monitored 

and verified twice daily temperature monitoring and verified 

high level of biosecurity • No horses tested • No clinical disease among exposed horses within 

14 day period • Adequate biosecurity verified by onsite inspection • Verified twice daily temperature monitoring with no 

fevers within previous 14 days. 

Isolate Onsite as far away 

from other horses as 

possible (minimum 30 feet)

Remains On Site 

NOT ISOLATED

Moved Offsite 

NOT ISOLATED

Recommend Movement Restrictions for EHM 

Suspect and Contact Regulatory Veterinarian

If negative 

pursue 

differentials

Assessment for Scope of Quarantine (Risk Assessment – See appendix)
IDOHC EHM Incident Guidance Document 52

Revised January 2018

RecommendedBiosecurityMeasures

foranEHMAffectedPremises

MonitoringHorses

RestrictAccessto

Exposed

LimitHorseto

HorseContact

EliminateSharing

ofEquipmentand

Personnel

Cleanand

Disinfect

IsolateNew

ClinicalCases

Immediatelyand

Contact

Regulatory

Official

QuarantineAnimals

and/orPremises

•RestrictMovement

andaccess

•PostVisible

QuarantineSignage

•Communicate

Quarantine

Parameterstoallon

premises(email,

phone,meeting)

•NotifyRegulatory

Officialofany

breachesin

Quarantine

•Obtainandrecordbody

temperaturesonallhorses

twicedaily(ideallyfirstthing

inthemorningandlast

thingintheevening)

•Reporttemperaturesof

101.5Ftoveterinarian

•Monitorallhorsesfor

compatibleclinicalsigns

(oculonasaldischarge,limb

edema,andneurologic

signssuchaswobblygait,

weakness,urinedribbling,

lackoftailtoneand

recumbency)

•Restrictpersonnel

accesstoonly

necessary

individualsforthe

careofexposed

horses

•Donotpermitdogs

inthehorsestabling

areas.

•Restrictvehicle

trafficfromhorse

stablingarea.

•Limitpotential

horsecontactin

commonareas

suchaswash

stalls,aisleways

andarenas.

•Avoidtyinghorses

tofencesorin

closeproximityto

eachother.

•Cleananddisinfectall

brushes,halter,crossties,

leadropesandtackwhich

havebeenpreviously

shared

•Useindividualequipment

foreachhorsetoavoid

sharing.

•Ifequipmentmustbe

sharedandcleanand

disinfectbeforeandafter

eachuse.

•Donotallowthehoseto

enterorcontactbucket

whenfillingwaterbuckets.

•Cleanallsurfacesofdirt

andmanurebefore

applyingdisinfectant

(10%bleachsolution)

•Completelycleanand

disinfectthestallof

infectedhorsesand

contaminated

equipment.

•Properdisposalof

potentially

contaminatedmaterials

•Encourageuseoffoot

bathswhichare

regularlycleaned.

IsolationParameters

•Isolateclinicalcasesatleast30feetfromallotherhorses.

•Restrictaccesstodesignatedindividualtocareforisolatedcase(shouldnothandleother

animalsontheproperty)

•Placefootbathandhandsanitizeroutsideeachisolationstallandrequireuse.

•Weardisposablegloveswhenhandlingisolatedhorses.

•Utilizedisposablecoverallsorchangeofclothesdesignatedforisolationareaonly

•Usedesignatedequipment(iestallcleaningsupplies,halter,feedtubs,waterbucketetc.)for

isolationareaonly

•Handleisolatedhorseslast.
IDOHC EHM Incident Guidance Document 53

Revised January 2018

NotificationofCase

Confirmationto

IndustryandState

AnimalHealth

Officials

MechanismsofCommunications

•WebsiteUpdate(dailyifhigh

profileEHMIncident)

•PressRelease

•EDCCUpdate

•SocialMedia

COMMUNICATIONSDURINGANEHMINCIDENT

(Within24hoursofinitialinvestigation)

ONSITECOMMUNICATIONS

(Recommendfacetoface

meetingofallentitiesattimeof

confirmation)

OFFSITE

COMMUNICATIONS

Veterinarian

HorseOwners/

Trainers

StableWorkers

Messages:

•AdviseonSampleType,Typeof

Test,Interpretationandwhich

populationtotest

•Requestassistancein

communicationstohorseowners/

trainers

Messages:

•Explaindiseaseagent,incubation

period,clinicalsigns,quarantine

restrictions,quarantinerelease

parameters

•Provideoverviewofbiosecurity

measurestobeimplimented.

Messages:

•Specificbiosecurityinstructions,

howtousefootbaths,howtoclean

anddisinfectequipment

•Explainimportanceofmeasures

andpotentialconsequences

CantheEHMincidentimpact

othersinthehorseindustry?

YESNO

Offsite

communicationsare

necessary

NOfurther

communication

isnecessary

Informationtocommunicate:

•Casedetails:Countylocation,indexhorseclinicalsigns,

diagnostictestresult(straintypesamplepositive),index

horsestatus(stableandbeingmonitored,euthanized,

recovering)

•RegulatoryAction:Quarantine,isolation,epidemiologic

investigation

•Recommendationsforexposedhorses
IDOHC EHM Incident Guidance Document 54

Revised January 2018

DetermineExposureRisk

AND

AssessmentofScopeofQuarantine

(SeeAppendixforExposureAssessment)

Horses

Exposed

10-14days

Ago

Horses

Exposed

3-10days

Ago

Tracetodetermine

potentialsourceof

infectiontoIndexEHM

Case

BUT

Noneedtomonitorfor

clinicalsigns

Monitorfor

ClinicalSigns

andTake

Temperature

TwiceDaily

for14days

fromlast

known

exposure

HighRisk

•DirectContactwithIndexEHMCase

•IndirectContactwithIndexEHMCase

•SharedStablingorifinsharedpastureordirect

contactpasture

•Sharedhalter,bit,bridle,leadrope

•Sharedgroomingequipmentsuchasbrushes

andwiperags

•Sharedfeedtubsorwaterbuckets

•SharedPersonnel(stallcleaners,grooms,

riders,farriers,etc)

•PoorBiosecurityManagementPracticesobserved

duringriskassessment

Seepremisesmatrixtodeterminespecificriskfactorsto

assessbasedonfacilitytype.

•NodirectcontactwithIndex

EHMcaseorLimitedtono

horsetohorsecontact

•Noindirectcontactwith

IndexEHM

•Immediateremovalor

IsolationofEHMcase

•Highbiosecuritystandards

verifiedduringrisk

assessment Lo

w

Risk

ReportFeveror

ClinicalSignsto

Veterinarian

ISOLATEANYHORSESHOWINGCLINICALSIGNS

AND

ContactVeterinarian

MinimalExposureRisk

DoesnotwarrantQuarantine

ModeratetoHighExposureRisk

ImplementQuarantine,EnhancedBiosecurity

MeasuresAndMovementRestrictions

EXPOSEDHORSEINVESTIGATION
IDOHC EHM Incident Guidance Document 55

Revised January 2018

MonitoringHorses

LimitAccessto

ExposedHorses

LimitHorseto

HorseContact

EliminateSharing

ofEquipmentand

Personnel

Cleanand

Disinfect

IsolateNew

ClinicalCases

Immediatelyand

Contact

Regulatory

Official

•Obtainandrecordbodytemperatures

onallhorsestwicedaily(ideallyfirst

thinginthemorningandlastthingin

theevening)

•Reporttemperaturesof101.5

0

Fto

veterinarian

•Monitorallhorsesforcompatible

clinicalsigns(oculonasaldischarge,

abortion,limbedema,andneurologic

signssuchaswobblygait,weakness,

urinedribbling,lackoftailtoneand

recumbency)

•Reportanycompatibleclinicalsigns

toveterinarian.

•Designateindividualtooverseehorse

healthtoensuretemperature

monitoringandobservationsare

completed.

•Keepwrittenlogofresultsof

monitoring

•Restrictpersonnel

accesstoonly

necessary

individualsforthe

careofexposed

horses

•Donotpermitdogs

inthehorse

stablingareas.

•Restrictvehicle

trafficfromhorse

stablingarea.

•Limitpotentialhorse

contactincommon

areassuchaswash

stalls,aisleways,tie

rails,andarenas.

•Avoidtyinghorsesto

fencesorinclose

proximitytoeach

other.

•Limitexposureto

respiratorysecretions

fromhorsesthatare

heavybreathing

during/afterexercise

•Avoiduseofcommunalwater

troughs

•Cleananddisinfectallbrushes,

halter,crossties,leadropesand

tackwhichhavebeenpreviously

shared

•Useindividualequipmentfor

eachhorsetoavoidsharing.

•Ifequipmentmustbeshared

thencleananddisinfectbefore

andaftereachuse.

•Donotallowthehosetoenteror

contactbucketwhenfillingwater

buckets.

•Cleanallsurfacesof

dirtandmanurebefore

applyingdisinfectant

(example:10%bleach

solution)Optimalto

washwithsoapand

waterthendisinfect.

•Completelycleanand

disinfectthestallof

clinicalhorsesand

contaminated

equipment.

•Properdisposalof

potentially

contaminatedmaterials

IsolationParameters

•Isolateclinicalcasesatleast30feetfromallotherhorses.

•Restrictaccesstodesignatedindividualtocareforisolatedcase(Ideally,shouldnothandle

otheranimalsontheproperty.Ifhandleotherhorsesonpremiseshandleisolatedhorseslast.)

•Placefootbathandhandsanitizeroutsideeachisolationstallandrequireuse.

•Weardisposablegloveswhenhandlingisolatedhorses.

•Utilizedisposablecoveralls,footwearcovers,glassesorasetofclothesandfootwear

designatedforisolationareaonly

•Usedesignatedequipment(iestallcleaningsupplies,halter,feedtubs,waterbucketetc.)for

isolationareaonly.

RecommendedBiosecurityMeasures

foranEHV-1ExposedHorses/Premises

CommunicatePlan

atalllevels
IDOHC EHM Incident Guidance Document 56

Revised January 2018

EHV-1 References

1. Maxwell, LK., Bentz, BG., Gilliam LL, etal. (2017) Efficacy of the early administration of valacyclovir 

hydrochloride for the treatment of neuropathogenic equine herpesvirus-1 infection in horses. 

American Journal of Veterinary Research, 78(10), 1126-1139

2. Dayaram A. etal (2017) Long term stability and infectivity of herpesviruses in water. Scientific 

Reports. 21 (7). 

3. Pusterla, N. etal (2016) Prevalence factors associated with equine herpesvirus type 1 infection in 

equids with upper respiratory tract infection and/or acute onset neurological signs from 2008 to 

2014. Veterinary Record, 178(3), 70.

4. Pusterla, N., Mapes, S., Wademan, C., White, A., Estell, K. and Swain, E. (2015) Investigations of the 

role of mules as silent shedders of EHV_1 during and outbreak of EHV-1 myeloencephalopathy in 

California. Veterinary Record. 

5. Pusterla, N. and Hussey, G.S. (2014). Equine Herpesvirus 1 Myeloencephalopathy. Vet Clin North Am 

Equine Pract.3, 489-506. 

6. Maxwell, L., Gilliam, L., Holbrook, T., Rezabek, G., Snider, T. and McFarlane, D. (2013) Prevention of 

Equine Herpes Myeloencephalopathy by Vaccination: A Pilot Study. AAEP Proceedings. 58, 51-52. 

7. Traub-Dargatz, J.L, Pelzel-McCluskey, A.M., Creekmore, L.H., Geiser-Novotny, S., Kasari, T.R., 

Wiedenheft, A.M., Bush,E.J., Bjork, K.E. (2013) Case-control study of a multistate equine herpesvirus 

myeloencephalopathy outbreak. J. Vet Intern Med., 27(2), 339-346. 

8. Burgess B.A., Tokateloff N., Manning S., Lohmann K., Lunn D.P., Hussey S.B., Morley P.S. (2012) Nasal 

Shedding of Equine Herpesvirus-1 from horses in an Outbreak of Equine Herpes 

Myeloencephalopthy in Western Canada. J. Vet Intern Med., 2, 384-392. 

9. Third International Havemeyer Workshop on Equine Herpesvirus type 1. 2012. Eq Vet J. 44, 513-517. 

10. “Awakening the Dormant Dragon: Neurological Form of EHV-1. White Paper on EHM” prepared by 

the Center for Equine Health and the School of Veterinary Medicine at University of California, 

Davis; May 2011. 

http://www.vetmed.ucdavis.edu/ceh/local_resources/pdfs/currenthealth_whitepaperEHM.pdf 

11. Pronost, S., Cook, R.F, Fortier,G., Timoney, P.J., and Balasuriya, U.B.R. (2010) Relationship between 

equine herpesvirus-1 myeloencephalopathy and viral genotype. Equine Vet. J. 42, 672-674. 

12. Lunn, D.P, Davis- Poynter, N., Flaminio, M.J., Horohov, D.W., Osterrieder, K., Pusterla, N. and 

Townsend, H.G. (2009) Equine herpesvirus-1 consensus statement. J. Vet Intern Med. J. Bet Intern 

Med. 23(3), 450-461. http://onlinelibrary.wiley.com/doi/10.1111/j.1939-1676.2009.0304.x/epdf 

13. Pusterla, N., Wilson, W.D., Madigan, J.E. and Ferraro, G.L. (2009) Equine Herpesvirus-1 

myeloencephalopathy: a review of recent developments. Vet. J. 180, 279-289. 

14. Pusterla, N., Wilson, W.D., Mapes, S., Finno, C., Isbell, D., Arthur, R.M. and Ferraro, G.L. (2009) 

Characterization of viral loads, strain and state of equine herpesvirus-1 using real-time PCR in horses 

following natural exposure at a racetrack in California. Vet. J. 179, 230-239. 

15. Allen, G.P. (2008) Risk factors for the development of neurologic disease after experimental 

exposure to equine herpesvirus -1 in horses. Am. J. of Vet. Research. 69, 1595-1600. 
IDOHC EHM Incident Guidance Document 57

Revised January 2018

16. Perkins, G.A., Goodman, L.B., Dubovi, E.J., Kim, S.G., and Osterrieder,N. (2008) Detection of Equine 

Herpesvirus-1 in Nasal Swabs of Horses by Quantitative Real- Time PCR. J. Vet Intern. Med. 22, 1234-

1238. 

17. Pusterla, N., Mapes, S. and Wilson, W.D. (2008) Use of viral loads in blood and nasopharyngeal 

secretions for the diagnosis of EHV-1 infection in field cases. Veterinary Record. 162, 728-729. 

18. Henninger, R.W., Reed, S.M. and Saville, W.J. (2007) Outbreak of neurologic disease caused by 

equine herpesvirus-1 at a university equestrian center. J. Vet. Intern. Med. 21, 157-165. 

19. Slater, J. (2007) Equine herpesviruses. In: Equine Infectious Diseases, 1st edn. Saunders Elsevier, St 

Louis, Missouri. pp 134-153. 

20. Hussey, S.B., Clark, R., Lunn, K.F., Breathnach, C., Soboll, G., Whalley, J.M. and Lunn, D.P. (2006) 

Detection and quantification of equine herpesvirus-1 viremia and nasal shedding by real-time 

polymerase chain reaction. J. Vet. Diagn. Invest. 18, 335-342.